A West Auckland mother who drove under the influence of methamphetamine and caused a crash that killed her daughter has avoided a jail term.

Toni Ericksen, 33, pleaded guilty before trial to driving while under the influence of drugs causing death, two charges of driving under the influence of drugs causing injury, and driving while forbidden.

She was today sentenced to 12 months home detention and 200 hours community service.

Bryer Greenwood, 12, was killed when the car Ericksen was driving crashed in Kaipara on July 9, 2011, while the family was returning from a netball game.

Ericksen's younger daughter Gemma, then 8, was also injured, along with the heavily pregnant passenger of the other vehicle.

Judge Roy Wade said he came into court "convinced" he would have to send Ericksen to prison.

He said he had been persuaded otherwise by lawyers.

Defence lawyer Peter Kaye said Gemma would be the one who suffered if Ericksen was sent to prison.

"She went through this accident. She was hurt and badly hurt. She woke up in hospital and still has recurrent nightmares. Social welfare decided to leave Gemma with her mother."

Prosecutor Emma Finlayson-Davis said the Crown acknowledged a prison sentence would affect the daughter who survived the crash but said similar cases had starting points of four to five years in prison.

A social worker's report said Ericksen had refused to be drug tested so it was not known if she had stopped using methamphetamine.

Kaye said stopping using drugs was something that happened gradually and his client had been praised for her progress.

He said it was a one-off accident and once she left the road onto the gravel "her fate was sealed".

Ericksen's car collided with another vehicle on the Kaipara Coast Highway, 2km north of Helensville.

She was forbidden from driving at the time and the car was not in a warrantable standard due to the baldness of three of her tyres.

Ericksen had to be cut from the wreckage of their car, which was "T-boned" by an oncoming 4WD, emergency services said at the time.

The driver of the other car was unhurt. The passenger successfully gave birth to her baby but had to do so by caesarean section due to the crash.

Judge Wade said Ericksen was "abusing and foul-mouthing" ambulance staff who attended the scene.